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Microstructure developments under fluorine plasma have been investigated in the Al2O3 ceramics containing artificial pores with controlled purity. The erosion behaviors by fluorine plasma consisted of a uniform erosion throughout the specimen surface and local erosions around the artificial pores and defects such as intrinsic irregular pores and damages formed during the grinding and polishing steps. The effects of the pores on the microstructure development were more distinct in the low purity Al2O3 specimen. The erosions around the pores, in the beginning, showed polygonal or flower-like microstructures in high or low purity Al2O3, respectively, indicating a weak grain boundary of glassy phase under the fluorine plasma. The extended plasma treatment resulted in loose structures around the pores in the low purity specimen, possibly producing contamination particles. In contrast to the polycrystalline Al2O3, single crystalline Al2O3 showed only uniform erosion. Although the microstructure developments were completely different depending on purity, porosity and polycrystallinity, etch depths did not appear so different, implying that the etch depths might not properly represent the plasma resistance of the materials.

Lactic acid bacterial strains were isolated from brines sampled after 7 days of an industrial sauerkraut fermentation, and six strains were selected on the basis of susceptibility to bacteriophages. Bacterial growth in cabbage juice was monitored, and the fermentation end products were identified, quantified, and compared to those of Leuconostoc mesenteroides. Identification by biochemical fingerprinting, endonuclease digestion of the 16S-23S intergenic transcribed spacer region, and sequencing of variable regions V1 and V2 of the 16S rRNA gene indicated that the six selected sauerkraut isolates were Leuconostoc fallax strains. Random amplification of polymorphic DNA fingerprints indicated that the strains were distinct from one another. The growth and fermentation patterns of the L. fallax isolates were highly similar to those of L. mesenteroides. The final pH of cabbage juice fermentation was 3.6, and the main fermentation end products were lactic acid, acetic acid, and mannitol for both species. However, none of the L. fallax strains exhibited the malolactic reaction, which is characteristic of most L. mesenteroides strains. These results indicated that in addition to L. mesenteroides, a variety of L. fallax strains may be present in the heterofermentative stage of sauerkraut fermentation. The microbial ecology of sauerkraut fermentation appears to be more complex than previously indicated, and the prevalence and roles of L. fallax require further investigation.Sauerkraut fermentation relies on naturally occurring lactic acid bacteria present on the raw cabbage. Several lactic acid bacterial species (mainly Leuconostoc mesenteroides, Lactobacillus brevis, Pediococcus pentosaceus, and Lactobacillus plantarum) are known to contribute to the complex sauerkraut fermentation process (28). L. mesenteroides is thought to be the dominant species in the early heterofermentative stage of this fermentation (13,14,28). However, there is little information available regarding the diversity of Leuconostoc species and strains involved in sauerkraut fermentation.In addition to L. mesenteroides, Leuconostoc strain DSM 20189 was isolated from cabbage fermentation (31); this strain was later identified as Leuconostoc fallax (25). L. fallax strains have been isolated from sauerkraut (18, 31), as well as from fermented rice cake (puto) in the Philippines (20) and from plant exudates of Gerbera jamesonii in The Netherlands (26). Two L. fallax strains have been isolated from exudates of G. jamesonii (26), and five different strains, divided into three pulsed-field gel electrophoresis patterns, have been isolated from fermented rice cake (20). L. fallax was the most prevalent species in puto fermentation, representing more than 20% of all of the isolates screened. Similar to cabbage, puto contains a diverse microflora, including both homo-and heterofermentative lactobacilli, and many different Leuconostoc strains are presumed to be responsible for the initial acid production (20).Several changes in the taxonomic classification of sp...

This paper presents the first report of bacteriophage isolated from commercial vegetable fermentations. Nine phages were isolated from two 90-ton commercial sauerkraut fermentations. These phages were active against fermentation isolates and selected Leuconostoc mesenteroides and Lactobacillus plantarum strains, including a starter culture. Phages were characterized as members of the Siphoviridae and Myoviridae families. All Leuconostoc phages reported previously, primarily of dairy origin, belonged to the Siphoviridae family.Commercial cabbage fermentations in the United States typically are carried out by epiphytic lactic acid bacteria (LAB), without the benefit of an added starter culture (8). Four species of LAB have been identified as the primary species involved in sauerkraut fermentations: Leuconostoc mesenteroides, Lactobacillus brevis, Pediococcus pentosaceus, and Lactobacillus plantarum (15). Pederson and Albury (12,13) determined that if the conditions of salt and temperature (2% NaCl and 18°C) are correct, a succession of these species will result in the consistent production of high-quality sauerkraut. For this reason, researchers have concluded that starter cultures are not needed for sauerkraut fermentations (14, 16).Our interest in studying the microbial ecology of sauerkraut fermentations has developed from the current need of the vegetable fermentation industry to reduce waste chloride production. Low-salt fermentation procedures are currently being developed as a means to reduce the chloride waste for sauerkraut fermentations (Fleming et al., unpublished). These procedures may require the use of starter cultures because lower salt concentrations may not result in the production of highquality sauerkraut (12).Bacteriophages active against all major LAB genera have been isolated and characterized (1), including phages of dairy origin active against Lactobacillus, Lactococcus, and Streptococcus species. In contrast, phages infecting other species of lactic acid bacteria have received relatively little attention. To our knowledge, the phages active against Leuconostoc have been characterized as belonging to the Siphoviridae family (1). Phages active against Oenococcus oeni (formerly classified as Leuconostoc oenos) isolated from wine fermentations have also been classified as Siphoviridae (14).The presence and ecology of bacteriophages in vegetable fermentations remain unexplored. Our objective was to identify bacteriophages in commercial cabbage fermentations, including one inoculated with a Leuconostoc mesenteroides starter culture.Sauerkraut fermentations were carried out at a commercial processing plant and consisted of one inoculated and one uninoculated tank, both of 90-ton capacity. L. mesenteroides LA10 was used as a starter culture; cells were grown overnight at 30°C in 8 liters of MRS broth containing 1% NaCl. The culture (10 9 CFU/ml) was then diluted to 76 liters with tap water and sprayed (20 to 40 lb/in 2 ) onto the sliced, salted cabbage as it was being conveyed on a belt to the fer...

Six bacteriophages active against Leuconostoc fallax strains were isolated from industrial sauerkraut fermentation brines. These phages were characterized as to host range, morphology, structural proteins, and genome fingerprint. They were exclusively lytic against the species L. fallax and had different host ranges among the strains of this species tested. Morphologically, three of the phages were assigned to the family Siphoviridae, and the three others were assigned to the family Myoviridae. Major capsid proteins detected by electrophoresis were distinct for each of the two morphotypes. Restriction fragment length polymorphism analysis and randomly amplified polymorphic DNA fingerprinting showed that all six phages were genetically distinct. These results revealed for the first time the existence of bacteriophages that are active against L. fallax and confirmed the presence and diversity of bacteriophages in a sauerkraut fermentation. Since a variety of L. fallax strains have been shown to be present in sauerkraut fermentation, bacteriophages active against L. fallax are likely to contribute to the microbial ecology of sauerkraut fermentation and could be responsible for some of the variability observed in this type of fermentation.Industrial sauerkraut fermentation relies on indigenous bacterial populations initially present on raw cabbage (42). Several members of the lactic acid bacterium family are known to contribute to the complex sauerkraut fermentation, including Leuconostoc mesenteroides, Lactobacillus brevis, Pediococcus pentosaceus, and Lactobacillus plantarum (42). Leuconostoc species, including L. mesenteroides and L. fallax, are known to be present and to be predominant in the early heterofermentative stage of this fermentation (7,24,25,36,42).Bacteriophage contamination is an important problem that is common in food fermentations, especially in the dairy industry. Among the bacteriophages that infect lactic acid bacteria, those specific for Streptococcus and Lactococcus species have been investigated most extensively (1). In contrast, little information is available on bacteriophages of Leuconostoc species. It was shown recently that phages active against lactic acid bacteria, including L. mesenteroides, L. plantarum, and P. pentosaceus, are present in pickle and sauerkraut fermentations (6, 57). Leuconostoc phages have also been identified as factors responsible for the failure of fermentations of several foods, including wine, coffee, and dairy products (4,9,18,19,27,28,39,48,49,50).Bacteriophages have the potential to control population levels and microbial diversity in natural bacterial communities (12). The interactions between bacterial and phage populations have been studied in dairy cultures (21), soil environments (17, 41), aquatic environments (8,11,12,29,54), and the phytosphere (5). To understand microbial succession and diversity in the complex sauerkraut fermentation, we must consider the roles and impact of bacteriophages.The primary objective of this work was to investigate the p...